Screening arrangement for screening immunoassay tests and agglutination tests

ABSTRACT

A screening device for performing an immunoassay test to detect the presence of a compound in a body fluid. The device includes a holder for removably receiving a membrane to which the fluid has been applied. A light is directed to the membrane. A photodetector measures the concentration of the light reflected back from the membrane. Specifically, the concentrations of reflected light from a control zone and a test zone are measured. Signals representative of the measured light concentrations are applied to a processor. If a specified concentration of predetermined light from a control zone on the membrane is detected, the processor considers the test to be successful. In the test is successful, the processor, based upon the measured concentration of reflected light from the test zone, generates data representative of the presence of the compound.

RELATIONSHIP TO EARLIER FILED APPLICATION

This application is a continuation of U.S. application Ser. No.11/151,147, filed Jun. 13, 2005, which is a continuation of U.S.application Ser. No. 09/760,374, filed Jan. 12, 2001, which is acontinuation-in-part of International Application PCT/GB99/02261,publication No. WO 00/04381, with an International filing date of Jul.14, 1999, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a screening device and methods of screeningimmunoassay tests and agglutination tests. In particular the inventionis applicable to a screening device for detecting the presence andconcentration of particular drugs in a sample of saliva.

Samples of bodily fluid such as blood, sweat, urine and saliva may beused to detect the presence of particular compounds, such as drugs, inthe body. Known methods of testing such samples for the presence ofcompounds include immunoassay “strip” testing where an antibody islabelled with a suitable marker, for example a visible marker such ascolloidal gold, and drawn along a membrane passing over test regions anda control region impregnated with analyte conjugate substances or otherbinding substances. The presence of particular compounds in the sampleare detected by a visible change occurring in the corresponding regiondue to the interaction of the labelled antibodies and the conjugatesubstances resulting in visible lines forming on the membrane in some ofthese regions. The colour formed may be proportional to or inverselyproportional to analyte concentration depending on the assay format.

The interpretation of the lines formed by such immunoassay testing haspreviously been carried out subjectively by an operator comparing theintensity of the test line (or the absence or presence of a line) withthat of a control, or reference, line.

U.S. Pat. No. 5,580,794 describes a disposable electronic assay device.For single analytes only one light source and detector is necessary; fortwo analytes, two sets of light source and detector is necessary and soon.

SUMMARY OF THE INVENTION

The invention in its various aspects is defined in the independentclaims below, to which reference should now be made, Advantageousfeatures are set forth in the appendant claims.

We have appreciated that in some fields of drug testing, for example inthe use of a sample matrix other than urine such as saliva or blood, theamount of drug present in the sample may be very low, and the operatormust be able to distinguish between a negative test corresponding to acomplete absence of the drug in the sample and very low levels of drugpresent. This is difficult, requiring highly trained and skilledoperators, and can prove unreliable when the levels of drugs are verylow. For example, it is particularly difficult for an operator todistinguish between levels of cannabis of 6 ng/mL or lower by eye. Ifthe test is to be run outside the laboratory, it is even more likely tobe subject to inaccuracies which may be exacerbated by poor lightingconditions or by other environmental factors. We have, therefore,recognised the need for a portable drug tester which produces reliableand reproducible results.

We have also appreciated that a non-invasive test that can be conductedfor example by the roadside would be beneficial. In a preferredembodiment of the invention we have therefore provided an automatic drugtester which can detect even very low levels of drugs from a salivasample.

Preferred embodiments of the invention are described with respect to thedrawings. In two of the preferred embodiments, immunoassay tests andagglutination tests run on samples of bodily fluid to detect thepresence of particular compounds such as drugs in the body may bescreened in the screening device. A test membrane is inserted into thescreening device and illuminated. The reflected image is detected andthe digitised data processed. For immunoassay tests, the digitised datais segmented and data for the test region is compared to that from thecontrol region and the background regions to determine whether the testdata exhibits any significant results. For agglutination tests, thedigitised data is processed to determine the number and size of theareas of coagulation to determine whether the test data exhibits anysignificant results.

In another preferred embodiment, a swab for taking a bodily sampleincorporates a run fluid capsule. Once an adequate sample of bodilyfluid has been collected and the swab is placed in contact with the testmembrane, the run fluid capsule is pierced by a spike provided on theswab, the run fluid mixes with the sample and the mixture is conveyed tothe test membrane. In another preferred embodiment, the swab has a maintube and a capillary tube. A run detector in the capillary tube detectswhen an adequate sample of bodily fluid has been taken.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described in moredetail, by way of example, with reference to the drawings in which:

FIG. 1 is an isometric view of a test cartridge;

FIG. 2 is a side view of an immunoassay test strip;

FIG. 3 is an isometric view of a preferred screening device embodyingthe invention with a test swab and test cartridge located ready foranalysis;

FIG. 4 is a side view of the screening device, test cartridge and testswab of FIG. 3;

FIG. 5 is a block diagram of the electrical controls and electricalapparatus used in the screening device;

FIG. 6 shows a graph of the typical variation of pixel intensity withpixel position for a single test and a single reference test;

FIG. 7 is a block diagram of the electrical controls and electricalapparatus which may alternatively or additionally be used in thescreening device;

FIG. 8 is a schematic view of the detected intensity of a test stripshowing the typical appearance of a control and test zone after a testhas been run;

FIG. 9 is a cut away side view of a second embodiment of a testcartridge;

FIG. 10 is a cut away side view of a second embodiment of a test swab;

FIG. 11 shows the cut away test swab of FIG. 10 inserted into a testcartridge and deployed for running a test;

FIG. 12 is a cut away side view of a third embodiment of a test swab;

FIG. 13 is a plan view of the test swab of FIG. 12;

FIG. 14 is a side view of the piercing spike for attachment to a testcartridge for use with the test swab of FIGS. 12 and 13;

FIG. 15 is a plan view of the spike of FIG. 14;

FIG. 16 is a flow chart showing the operation of a second embodiment ofthe screening device;

FIG. 17 is a schematic diagram showing the correspondence between thesequence of the element-wise processing of the monochrome data array andthe position in the acquired image;

FIG. 18 is a flow chart showing the primary scan operation of FIG. 16;

FIG. 19 is a flow chart showing the secondary scan operation of FIG. 16;

FIG. 20 is a flow chart showing the tag tree compaction andsimplification operation of FIG. 16;

FIG. 21 is a plan view of a single reaction agglutination testcartridge; and

FIG. 22 is a plan view of a multiple reaction agglutination testcartridge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a test cartridge 10 used to run the immunoassay tests to bescreened by the screening device. The test cartridge 10 may bedisposable and is formed from a top 12 and a base 14. The top 12 of thetest cartridge 10 has a cylindrical swab holder 16 extending verticallyfrom one of the shorter ends of an elongate tray 18. The swab holder 16is open at both ends.

Ridges 20 extend upwardly from both of the longer sides of the elongatetray along the length of the tray. A rectangular window 22 extendstransversely between the ridges 20 across the elongate tray and extendsover a longitudinal length of the elongate tray which is less than theoverall length of the elongate tray such that the window 22 is boundedon all four sides by the elongate tray 18. The window 22 extends throughthe entire thickness of the elongate tray 18.

FIG. 2 shows an immunoassay test strip 23. The upper surface of a flat,elongate nitrocellulose membrane 24 is bonded to a waste pad 28 at oneend and to a conjugate release pad 27 at its other end. Both theconjugate release pad 27 and the waste pad 28 overlap the ends of thenitrocellulose membrane 24. The other end of the conjugate release pad27 overlaps an absorbent sample pad 26 and is bonded at its uppersurface to the lower surface of the absorbent sample pad 26. When fluidis applied to the sample pad 26 it is drawn along the sample pad bycapillary action, through the conjugate release pad 27 andnitrocellulose membrane 24 and surplus fluid is absorbed by the wastepad 28.

The base 14 of the test cartridge 10 has a rectangular portion with arounded portion at one end. An immunoassay test strip 23 is laid ontothe upper surface of the base 14 with the sample pad 26 located in therounded portion of the base 14. The immunoassay strip 23 (shown indashed lines on FIG. 1) extends longitudinally along the length of thebase 14 from the end of the base furthest from the rounded portionstopping within the rounded portion but short of the end of the roundedportion. The top 12 is then assembled onto the base 14 by fitting thecylindrical swab holder 16 onto the rounded portion of the base 14 andthe elongate tray 18 of the top 12 onto the rectangular portion of thebase 14. The top 12 and base 14 are joined for example by gluing.Alternatively, the top 12 may be designed to snap-fit onto the base 14.The top 12 may be made of a single unit so that the elongate tray 18 andthe swab holder 16 are a single piece.

The conjugate release pad 21 holds a mobile and visible label, ormarker, such as colloidal gold, and is in contact with thenitro-cellulose membrane 24 such that when fluid is added to the swabholder 16, it is drawn by capillary action downstream from the swabholder 16 through the absorbent sample pad 26 through the conjugaterelease pad 27 and subsequently through the nitro-cellulose membrane 24.The use of cartridges of this type is known in the prior art for examplefrom EP 0291 194 by Unilever NV titled “Immunoassays and devicestherefor”.

At discrete intervals along the nitro-cellulose membrane 24 drug-proteinderivatives are biochemically bound to the nitro-cellulose membrane,producing an immobile test zone of drug-protein derivative which spansthe width of the nitro-cellulose membrane. Towards the extremedownstream end of the nitro-cellulose member, downstream of all theimmobile drug-protein derivative test zones, is a control zone whichalso spans the width of the nitro-cellulose membrane. The test zones andcontrol zone are interposed between background zones where thenitrocellulose membrane 24 does not have bound drug conjugate but hasbeen blocked by other protein or other substances to preventnon-specific binding. Antibodies to each drug which is to be tested for,conjugated with colloidal gold, are placed on the conjugate release pad27. When saliva is transferred from the swab in the presence of arun-fluid, the resulting sample passes across the absorbent sample pad26 and across the conjugate release pad 27 where it mixes with theantibody-gold conjugates. The sample then travels the length of thenitro-cellulose membrane 24.

If the particular drug is present in the sample it will bind to theantibody-gold conjugate. When the bound drug subsequently passes overthe specific drug-protein derivative test zone the antibody-goldconjugate has already been bound to the drug in the sample and is notfree to bind with the drug-protein derivative bonded to the membrane. Ifthe particular drug is absent from the sample, the antibody-goldconjugate will be free to bind to the drug-protein conjugate at thespecific test zone causing the antibody-gold conjugate to becomeimmobilised at the site of the drug-protein conjugate. The visiblemarker is deposited in the test zone as a coloured line or stripe. Inbetween these two extremes some of the antibody-gold conjugate will bindwith the drug-protein derivatives at the test zone on the strip creatingan intermediate intensity of colour. The intensity of the colour on theparticular drug-protein test zone is therefore inversely proportional tothe amount of drug present in the sample.

The depth of colour of the control zone should always be significant andthe control zone is designed with this in mind. The colour of thecontrol zone can then be used to indicate that the assay test has beensuccessfully run and to threshold colour levels in specific drugconjugate test zones.

FIG. 3 shows the test cartridge 10 of FIG. 1 located into the screeningdevice 30. The screening device 30 includes a receiving section, animaging section and a display section. The receiving section is locatedat the rear of the screening device and receives and aligns a testcartridge prior to the screening operation. The imaging section islocated centrally in the screening device between the receiving sectionand the display section and includes the illuminating and imagingequipment, the processing capabilities and battery pack. At the front ofthe screening device is the display section for outputting the resultsof the screening operation. A cover (not shown) which is open at thefront end of the screening device 30 encases the remaining five sides ofthe screening device 30. A facia cover (not shown) is attached to thecover to completely encase the screening device 30, protecting thescreening device and the user from accidental damage.

The receiving section includes a receiving bracket 32 and a microswitch43 and also positions and supports a half silvered mirror 40 which formspart of the imaging section. The receiving bracket 32 has a back 38 andtwo parallel arms 36. The back 38 is connected at either end to one endof each arm forming a U-shaped bracket. The open end of the U-shapedreceiving bracket 32 is directed outwardly from the screening device 30and is aligned with an opening in one side of the cover (not shown)towards the rear of the screening device 30. The opening is large enoughto allow a test cartridge 10 to be inserted into the bracket 32 of thescreening device 30. The arms 36 of the receiving bracket 32 are spacedapart by a distance equal to the width of the test cartridge 10 and havethe same longitudinal length as that of the elongate tray 18 of the testcartridge 10. The arms 36 have a C-shaped cross-section. When a testcartridge is inserted into the opening the ridges 20 on the testcartridge 10 engage with the C-shaped cross-section of the arms 36 ofthe receiving bracket 32 to direct the test cartridge into the screeningdevice 30. The test cartridge 10 is slidably inserted into the arms 36of the bracket 32 of the screening device 30 until the end of the testcartridge reaches the back 38 of the receiving bracket when pressureagainst further insertion will be felt.

A half silvered mirror 40, which forms part of the imaging section ofthe screening device, is supported above the window 22 of the testcartridge 10 by a column 42 extending upwardly from the outer arm 36 ofthe receiving bracket 32 nearest the rear of the screening device 30.

A test swab 70, which functions as a collecting device for a salivasample, is located in the swab holder 16 of a disposable test cartridge10. The test cartridge 10 is inserted into the screening device 30 bythe end furthest from the swab holder 16 and is positively located inthe correct screening position by receiving bracket 32. The back 38 ofthe receiving bracket 32 prevents the test cartridge 10 from beinginserted too far into the screening device 30 and ensures that thewindow 22 of the cartridge 10 is located directly in front of andbeneath the CCD 34 of the screening device 30. Electrical circuitry 50controlling the operation of the screening device including operation ofthe CCD 34 are housed within the screening device 30 towards the frontof the screening device 30 in front of the CCD 34, test cartridge 10,and rechargeable batteries 48.

A microswitch 43 is supported above the test cartridge 10 from the innerarm 36 of the receiving bracket 32 nearest the CCD 34. When a testcartridge 10 is fully inserted into the screening device 30 themicroswitch 43 is displaced vertically causing an electrical signal tobe emitted from the microswitch to signal that the correct insertion ofa test cartridge 10 has been detected. During screening of the testcartridge 10, the microswitch 43 may resist any displacement of the testcartridge 10 once it has been fully inserted into the screening device.

The imaging section includes illuminating means, photosensitive detectormeans, means for representing the intensity of the detected light by adata array, data processing means for segmenting the data and comparingthe segmented data and output means. The illuminating means is providedby three light emitting devices (LEDs) 44 which are mounted in ahorizontal line parallel to the longitudinal length of the testcartridge 10 with the middle LED centred vertically above the centre ofwindow 22 of the test cartridge 10. The photosensitive detector meansand means for representing the intensity of the detected light by a dataarray are provided by the CCD 34 which includes an imager 82, a videodigitiser 84 and a video data interface 86 (shown on FIG. 5).Alternatively, the photosensitive detector means may be made up from aCCD array device together with a control and data conversion interface.The imager of the CCD 34 is directed towards the rear of the screeningdevice 30. A mounting plate 46 is attached to the upper body of the CCD34 towards the front of the screening device 30. The mounting plate 46extends horizontally from the body of the CCD 34 towards the rear of thescreening device 30 and finishes directly above the window 22 of thetest cartridge 10. Three LEDs 44 are attached in a row at the front ofthe underside of the mounting plate 46. When illuminated, the light fromthe LEDs 44 shines directly onto the window 22 of the test cartridge 10.The mirror 40 is inclined from the vertical by approximately 35° suchthat the window 22 of the test cartridge is reflected into the field ofview of the CCD 34. Light reflected from the immunoassay test isdetected by an array of photosensitive detectors in the imager 82. Thephotosensitive detectors emit an electrical signal proportional to theintensity, the concentration of light detected. The video digitiser 84scans each of the photosensitive detectors in turn, converting theanalogue data to digital data and storing the data in an array. Thearray of digital data is subsequently outputted to a central processorunit (CPU) 80 via the video data interface 86.

Rechargeable batteries 48 supply power to the CCD 34, LEDs 44,microswitch 43 and electrical circuitry 50. The rechargeable batteries48 are positioned towards the front of the imaging section below the CCD34. The electrical circuitry 50 which forms the final part of theimaging section is described later with reference to FIG. 4 and FIG. 7.

At the front of the screening device 30 is the display section includingtwo test indicator LEDs 52 and 54, a liquid crystal display device (LCD)56, operating buttons 58 and 60 and a front plate 62. The front plate 62is slightly smaller than the facia cover and is located at the front ofthe screening device 30 directly behind the facia cover. The two testindicator LEDs 52 and 54 are mounted at the top of the rear of the frontplate with the LEDs 52 and 54 protruding above the level of the frontplate 62. Holes in the top of the cover at its front corner allow thetest indicator LEDs 52 and 54 to protrude through the cover such thatthey are visible on top of the device.

The LCD 56 and its associated backlight driver 94 are mounted at the topof the front plate 62 between the front plate 62 and the facia cover.The facia cover has a window through which the LCD 56 is visible butwhich obscures the backlight driver 94, located behind the LCD 56, fromview. Also mounted onto the front plate 62 between the facia cover andthe front plate are the two operating buttons 58 and 60. The facia coverhas holes in corresponding locations to allow the user to operate thebuttons 58 and 60 through the facia cover.

Additionally holes for an infra-red communication port and a serial andparallel link for connecting the screening device to a personal computer(PC) may be provided in the cover and corresponding connections from theelectrical circuitry 50 may be provided.

FIG. 4 shows a partially sectioned side view of the screening device ofFIG. 3.

FIG. 5 shows a block diagram of the electrical components of thescreening device 30. The screening device 30 is based around amicroprocessor or central processor unit (CPU) 80 and the CCD 34. TheCCD 34 comprises the imager 82, and associated video digitiser 84 andvideo data interface 86. The screening device may also includes a keypad88 or may be operated via a combination of buttons provided on thefacia. The screening device also includes electrically erasable readonly memory (EEPROM) 90, dynamic random access memory (RAM) 92 and theliquid crystal display (LCD) 56. The EEPROM 90, RAM 92 and LCD 56 areconnected to the CPU 80. Alternatively, the EEPROM and RAM may beinternal to the CPU. The LCD 56 may be backlit and control is providedvia a backlight driver 94 which is connected to both the CPU 80 and theLCD 56.

The keypad 88 may be used to allow a user to enter data required by theCPU 80 to control operation of the screening device. Results from thescreening device 30 are displayed to the user via the LCD 56 which alsoacts to prompt the user for the data required to operate the screeningdevice. Power is supplied to the CPU 80, LEDs 44, LEDs 58 and 60,microswitch 43 and CCD 34 from the rechargeable battery pack 48. Thebatteries can be recharged from the main electrical supply or, forexample from a car cigarette lighter, via an adaptor. The operation ofrecharging the batteries can be controlled by the CPU or alternativelycan be controlled manually. Preferably, the screening deviceautomatically shuts down to preserve battery life if no cartridge ispresent or if the results of the previous screening have been displayedfor longer than a preset time, say 5 minutes. Preferably, if an externalpower supply is detected by the screening device the CPU 80automatically commences a battery recharging program. Preferably, thebatteries can hold enough charge to operate continuously for up to 24hours without being recharged.

The CPU 80 controls an electroluminescent backlight driver 94 tobacklight the LCD 56. Preferably, the LCD 56 is capable of displayingtwo rows each of 8 alphanumeric characters. In addition to the LCDdisplay, two LEDs, one red 58 and one green 60, are provided.Illumination of the LEDs 56 and 60 is controlled by the CPU 80 and maybe used is to indicate visually the progress and status of the scan, iein progress, results ready for display, or the outcome of the test.Alternatively, the progress or results could be indicated by an audiblesignal. The LCD 56 may also display status information.

In the embodiment described above the overall size of the device isapproximately 85 mm by 80 mm by 65 mm and the device weighsapproximately 300 g. The test device is thus small, light weight, andportable. The CCD 34 may be, for example, a Connectix Quickcam,incorporating a CCD imager, video digitiser and video data interface.

Operation of the screening device will now be described. Disposablesaliva test swabs 70 are stored in a sealed pack and one swab removedimmediately prior to use. The swab should be removed from the pack bythe person whose saliva is to be tested and is wiped under the tonguefor approximately 15 seconds. The swab 70 is then inserted into the swabholder 16 of a disposable test cartridge 10. Ten drops of a run fluid,which may be of any conventional type, are added to the swab holder 16.The run fluid transports the sample of saliva from the test swab 70 tothe absorbent pad 26 and onto the conjugate release pad 27, where thesaliva and run fluid mixture mixes with the labelled (e.g. with gold,coloured latex particles, carbon particles, fluorescents, or any othersuitable label) anti-drug antibodies. The sample subsequently travelsalong the length of the nitro-cellulose membrane 24. At each test zoneany unbound labelled drug antibodies are bound to the drug-proteinderivative of the test zone. Any of the labelled antibodies which havenot been bound to the test zones passes over the control zone where itbecomes bound to the control zone. The result is a number of lines ofvarying intensity spanning the width of the membrane at points along thelength of the nitro-cellulose membrane corresponding to the drug-proteinderivative test zones and the control zone. Each drug-protein derivativetest zone can be used to detect a different drug. The higher theconcentration of the particular drug in the saliva sample, the lessintense the colour in that drug-protein derivative test zone.

As soon as the test swab 70 has been located in the swab holder 16 thetest cartridge 10 is inserted into the screening device by gentlypushing the end of the cartridge furthest from the swab holder 16 intothe opening of the screening device 30, allowing the test cartridge 10to be guided by the receiving bracket 32. The test cartridge 10 shouldbe inserted gently until the end of the test cartridge furthest from theswab holder 16 reaches the back 38 of the receiving bracket 32 whenthere will be resistance against further insertion.

Once inserted into the screening device the cartridge is left inposition until the scanning process has been completed. A message on theLCD and/or flashing of the LEDs indicates that the scan is complete.Only then may the cartridge be removed.

As the test cartridge 10 is pushed into position it displaces the microswitch 43. A signal is sent from the microswitch 43 to the CPU 80 whichactivates the scanning process by down-loading a preset program fromEEPROM 90. Timer means are provided to delay illumination of theimmunoassay test strip until the test has had time to run. Once thepresence of a test strip has been detected the CPU 80 commencesinitialisation by prompting the user to set a timer to alert theoperator to wait a sufficient time for the sample to travel the lengthof the membrane. Alternatively the user may time the test manually andan on/off power switch can be provided which the user can operate oncethe assay test has been run and the test cartridge 10 has been insertedinto the screening device 30. The timer function may be provided by aseparate timer integrated circuit controlled by the CPU 80 or mayalternatively be provided internally to the CPU 80. When theprerequisite length of time has elapsed, which is generally of the orderof five minutes, the timer sends a signal to the CPU 80 which alerts theoperator that the sample is ready for screening for example by flashingLEDs 58 and 60, displaying a message on LCD 56 or sounding an alarm. Thescreening device is also able to time the test, analyse results, outputresults and store the results automatically.

A plurality of adjacent membranes may be incorporated into a single testcartridge with the membranes running longitudinally the entire length ofthe cartridge from the absorbent pad to the end of the cartridgefurthest from the swab holder and each membrane 24 having a transversewidth less than that of the test cartridge 10 such that a plurality ofmembranes, for example two, may be placed side by side in the testcartridge 10. Processing the results of the saliva test depends onidentifying the intensity of the lines on each membrane and relatingeach line to the drug which is the subject of that particular test.Details of the number of adjacent membranes in the particular cartridgeand the number, type and position of the drug-protein derivative zonesand control zone on each membrane are required for processing of theresults. These details can be held in the EEPROM and accessed by the CPU80 upon detection and recognition of the cartridge type or the user candirectly enter data required for the CPU 80 to recognise the testcartridge 10. If the test cartridge 10 is to be recognised by the CPU 80it may carry appropriate marking such as a bar code, which is read byappropriate means provided in the screening device and the informationis passed to the CPU 80.

The test cartridge 10 may be printed with the name of the test which maybe automatically read and identified by the CPU 80. The test cartridge10 may also contain an implanted microelectronic circuit which may beinterrogated by the CPU 80 by means of electrical, infra-red orinductive links in order to ascertain whether the cartridge isacceptable and to determine the nature of the test.

The CPU 80 enables the CCD 34 and switches on the appropriate LED 44,thus illuminating the window 22 of the test cartridge 10. In thepresently preferred embodiment three LEDs are provided, with wavelengthsof 430 nm, 565 nm and 660 nm respectively. The wavelength of lightemitted by each LED is chosen with reference to the characteristics ofthe label, in particular to its colour. Preferably the wavelength of thelight used to illuminate the immunoassay strip is complementary to thewavelength of the particular label in order to provide the bestcontrast. In the presently preferred embodiment, colloidal gold isemployed as the label and as colloidal gold is pink in colour a greenLED with a wavelength of 565 nm is used. Whilst the label has beendescribed as visible and the example of colloidal gold as a label wouldbe visible to the human eye, the label may be chosen to be visible tothe CCD array under certain lighting conditions and may not, eitherunder normal lighting conditions or under special lighting conditions,be visible to the human eye.

Light from the LED 44 shines onto the window 22 of the test cartridge 10illuminating the nitro-cellulose membrane 24 visible through the window22. The illuminated membrane 24 is reflected by the mirror 40 into thefield of view of CCD 34. The image is digitised and outputted via avideo data interface to the CPU 80 for data processing. Preferably, thedigital data is stored to dynamic RAM 92 for subsequent processing.

The image captured by the CCD 34 is skewed by the reflection from themirror 40 and the CPU 80 must first apply an algorithm to correctlyalign the digitised data for processing. Preferably, the CPU 80 runs aninitial is correction algorithm to arrange the data for subsequentprocessing. Preferably the initial correction algorithm is set when thedevice is manufactured and, if necessary, calibrated, at points duringthe life of the device rather than at the beginning of each test.

Each cartridge may be used to run tests for a number of different drugs.This can be achieved either by using a single membrane with a largernumber of drug-protein derivative zones or using a number of membranesin a single cartridge. Up to eight or more drugs may be analysed at anyone time using a combination of these methods. In the presentlypreferred embodiment, drug-protein derivatives for cannabis (THC),cocaine (COC), opiates (OPI), methadone, ecstasy and amphetamines (XTC)and benzodiazepines (BZO) are bound to the nitro-cellulose membrane atdiscrete intervals. The results for each of these drugs tests isindicated separately by the screening device. Two panel tests, forexample for methadone and opiates, may also be provided. The data mustthen be segmented such that each segment relates to one membrane only.The separate segments are then processed separately. In the presentlypreferred embodiment the CCD array is a Texas TC 255 P CCD array whichis made up of 324×240 elements. The digital data must be segmented tocorrespond to the 344×240/N pixels covering that particular membraneonly where N is the number of membranes in the cartridge.

Each membrane is therefore represented by an array of p×q pixels wherethe p pixels span the length of the membrane and the q pixels span thewidth of the membrane. The drug-protein derivatives are bonded acrossthe entire width of the membrane at discrete intervals along themembrane. At any location (p,r) where p falls within a particulardrug-protein derivative test zone the intensity of the pixel is relatedto the amount of that particular drug in the sample, regardless of thevalue of r in the range 0≦r≦q. The intensities of the pixels at (p,r)are therefore summed over the range 0≦r≦q for each p.

Slight discrepancies between the theoretical position of the membraneand the actual position of the membrane may be accommodated by thescreening device. The CPU 80 compares the summed intensity at a specificlocation corresponding to the theoretical centre position of the controlzone with the intensity at a predetermined number of adjacent locationsto determine whether there is any discrepancy between the theoreticallocation of the control zone with the actual location of the controlzone. The CPU 80 applies a corresponding offset to subsequentcalculations if the theoretical and actual locations of the centre ofthe control zone differ. The offset must be determined by reference tothe control zone because if any of the tests are positive then theintensity of that drug-derivative test zone will be correspondinglyreduced.

Alternatively, or in addition, the test strip 23 and test cartridge 10may be of contrasting colours. The unskewed data may be processed usingthe contrast between the test cartridge 10 and the test strip 23 todetermine the actual location of the centre of the test strip which maythen be used to apply an offset to the data if required.

FIG. 6 shows a typical graph of the resulting pixel intensity againstthe location of the pixel for a single protein-drug derivative test zoneand a single control, or reference, zone. Once any offset of themembrane from the theoretical position has been identified, the data issegmented according to whether it lies in a drug-protein derivative testzone, the control zone or in a space (i.e. a background zone) betweenadjacent zones as shown in FIG. 6. Preferably, the CPU 80 is a HitachiH8/3002 microprocessor chip but any other suitable microprocessor chipmay be used. The CPU 80 segments the data into a first plurality of datacorresponding to the control zone, a second plurality of datacorresponding to the test zones, and a third plurality of datacorresponding to the background zones. The CPU 80 then processes thefirst, second and third pluralities of data, performing the followingcalculations to determine whether each drug is present in the sample.

Define

${{RW}\; 1} = {{\sum\limits_{p\; 1}^{p\; 2}{RB}} = {{\sum\limits_{p\; 2}^{p\; 3}{{RW}\; 2}} = {\sum\limits_{p\; 3}^{p\; 4}{and}}}}$${{TW}\; 1} = {{\sum\limits_{p\; 5}^{p\; 6}{TB}} = {{\sum\limits_{p\; 6}^{p\; 7}{{TW}\; 2}} = \sum\limits_{p\; 7}^{p\; 8}}}$

Then estimate

${REF} = {1 - \left( \frac{2{RB}}{\left( {{P\; 3} - {P\; 2} + 1} \right)\left( {{{RW}\; 1} + {{RW}\; 2}} \right)} \right)}$and${TEST} = {1 - \left( \frac{2{TB}}{\left( {{P\; 7} - {P\; 6} + 1} \right)\left( {{{TW}\; 1} + {{TW}\; 2}} \right)} \right)}$

If REF≦0 then the reference, or control, zone has not bound any of theproducts present in the saliva sample and run fluid after it passed overthe drug-protein derivative test zones. Either the control zone isfaulty on the membrane or the assay test has not been completedcorrectly which may be due to an insufficient amount of run-fluid beingadded to the swab holder. The screening device will display an errormessage and the cartridge should be removed, reinserted and reread ordisposed of and another cartridge run. However, the delay for the testto be performed is not required in these circumstances and the operatoris provided with a means for bypassing the timer operation to commenceimmediate image acquisition and data processing. If an error is stilldetected then the test must be re-run using a new cartridge and salivasample.

If REF>0 showing that the assay test has been successfully completed butTEST≦0 then the drug concentration in the sample is such that all theantibody-gold conjugates have been bound to the drug in the sample. Theresults of that test is set to 100%. The test is assigned a qualitativelevel “Positive”. A quantitative value would be represented as “greaterthan” a certain level.

If TEST>0 and REF>0 then the test band concentration is determined asfollows:

${{TEST}\mspace{14mu} {BAND}\mspace{14mu} {CONCENTRATION}} = {1 - \left( \frac{TEST}{REF} \right)}$

The percentage of drug present in the sample is given by 100× Test Bandconcentration %.

The results for the concentration of each drug can be displayed in anumber of ways. The LCD 56 may be used to display the name of the drugand its result. Alternatively only the fact that the test for thatparticular drug is positive may be displayed. If the display is toindicate a positive or negative result only then the CPU 80 must haveaccess to a threshold for each drug which could be held in the EEPROM.For each drug if the detected concentration exceeds the threshold thenthe result would be positive and if the detected concentration fallsbelow the threshold then the result would be negative. Each separatedrug-protein test zone must be tested in this way with reference to thecontrol zone to determine the concentration of that drug in the salivasample.

Alternatively, or in addition, positive and negative results could bedisplayed using combinations of the LEDs 52 and 54 provided on the topof the screening device. In the presently preferred embodiment, the redLED 52 will be continuously illuminated and the green LED 54intermittently illuminated to indicate that the particular drug test ispositive, and the green LED 54 will be continuously illuminated with thered LED 52 flashing if the drugs test is entirely negative. The operatormay step through the result of each individual drug test by operatingthe buttons 58 and 60 on the front of the screening device or may viewall the results simultaneously by down loading the results to a pc withthe necessary graphics facilities. Results may be stored within thescreening device until they are down-loaded to a PC. The test image maybe stored for subsequent downloading to a PC.

If the test indicates that any of the drugs are present in the sample,follow up testing using an alternative test method may be performed.

The CPU 80 is provided with a programming interface 98 to allow thescreening device to be programmed for example from a remote PC. Serialand parallel PC links 96 and/or an infra-red link may provided from theCPU 80 allowing the control of the screening device to be relinquishedto a pc or mainframe computer. Results of the testing can also bedisplayed by the pc having been down loaded from the screening device.Preferably, the CPU 80 is capable of running self-testing diagnosticroutines stored in EEPROM at intervals which may be controlled either bypresets in the CPU or may be initiated on demand by the user.

In certain situations it may be preferable for the screening deviceoperator to be provided with a display indicating the image produced bythe CCD 34. An interface for the CCD 34 may be provided to allow theoperator to view the image on a small graphics panel.

It may also be preferable to provide means for storing the image of theperson who provided the test sample. For this purpose, the mirror 40could be adjusted between the test screening position and a secondposition which allowed the image of the person being tested to bereflected onto the imaging means for storage and subsequent retrieval.Additional optical apparatus, for example a lens, may be required tomodify the focal length along the external light path.

FIG. 7 shows a block diagram of the electrical controls and electricalapparatus which may also be used in the screening device. Apparatus andcontrols which correspond to those of FIG. 4 are given the samereference numerals and reference should be made to the descriptionabove.

In particular, a CMOS image sensor 82′ may be used instead of a CCDimage sensor. A driver is associated with the CMOS image sensor 82′ andinterfaces between the CPU 80 and CMOS image sensor 34′. A video buffer86′ replaces the video data interface 86 of FIG. 5. Preferably, a VisionVV5404 imaging device having a resolution of 356×292 pixels is used.

The electroluminescent backlight driver 94 shown in FIG. 5 may also bereplaced by light emitting diode backlight driver 94′. Furthermore, thevolatile memory device 90 provided by an EEPROM in the apparatus of FIG.5 may be replaced by FLASH memory and/or the non-volatile memoryprovided by the dynamic RAM (DRAM) in FIG. 5 may be replaced by staticRAM (SRAM). An LCD 56′ with a higher resolution capable of handlinggraphics of 100×64 pixels may also replace the LCD 56 of FIG. 5. Thiswould allow all the test results to be displayed simultaneously ifrequired. Batteries which are capable of holding sufficient charge topower the screening device for up to 20 days may be provided.

Preferably, means 45 for adjusting the intensity of each of the LEDs 44may be provided. Adjustable current LED drivers may be used as shown inFIG. 7.

The half silvered mirror 40 of FIGS. 3 and 4 may be replaced by a plainfirst surface mirror 40. The angle of the mirror and the imaging devicemay be altered to reduce the skew of the image. For example, byadjusting the angle of the mirror 40 to 55.degree. to the vertical andusing a CMOS image sensor inclined at 10.degree. to the vertical, thecombined inclination of the CMOS image sensor 82′ and the mirror 40minimises the difference in the image width over the width of the teststrip with the result that the image captured by the CMOS image sensor82′ is substantially unskewed relative to the actual immunoassay teststrip 23. In the case that the image captured by the imaging device isunskewed, the CPU 80 is not required to apply an algorithm to correctthe digitised data prior to processing the data.

Different numbers of LEDs 44 may be used to illuminate the test strip23. For example, four LEDs rather than three may be mounted in ahorizontal row parallel to the longitudinal length of the testcartridge. If four LEDs are used, the two outermost LEDs may be chosento emit light of one wavelength whilst the two innermost LEDs may bechosen to emit light of a different wavelength. With this configuration,only one pair of LEDs may be used to illuminate the immunoassay teststrip 23 for the purpose of determining the drug concentration. Theremaining pair of LEDs may be used for non-disruptive messaging, forexample reading a bar code on the test strip or cartridge. Theintensities of the LED pairs may be matched to provide optimalillumination of the immunoassay test strip 23. Suitable wavelengths forthe LED pairs are 566 nm and 639 nm. However, the primary requirement inchoosing suitable LEDs is that the wavelength of light emitted iscompatible with the marker used on the immunoassay test strip 23 andthat illumination of any messaging markings does not corrupt the testresults.

The size and weight of the screening device may be affected by thechoice of electrical apparatus and controls. Using a Vision VV5404, theoverall dimensions and weight of the screening device may be 210×70×50mm and approximately 240 g.

The control band may only be used to verify that the test has runsuccessfully and may not be used for the quantification of individualdrug concentration calculations. In this case, null data, referencedata, may be provided in order to quantify the test results. Such nulldata may, for example, correspond to the data which would be generatedby illuminating a blank immunoassay test strip under identicalconditions to the illumination of the experimental immunoassay teststrip. Such null data would then give an estimate of the intensityobserved when the concentration of a drug in the sample under testapproximates or exceeds the amount of conjugated antibodies releasedfrom the relevant pad. Such null data may be compared to the test datato determine the concentration of the substance in the sample undertest.

Null data may be approximated by suitable filtering of the experimentaldata eliminating any need for separate illumination of an unused, cleantest strip as a reference strip. For example, data corresponding to thelength and width of one of the background zones may be interpolated toproduce an estimate of the intensity that is representative of nulldata. Prior to interpolation, the data may be smoothed to improve thenull data. More sophisticated filtering techniques, including adaptivefiltering, may also be used in estimating the null data. Once null datahas been estimated or provided, the test data and null data maytherefore be compared to determine the concentration of the substancesin the test zones.

FIG. 8 shows schematically typical results of the appearance of acontrol zone and test zone thus detected by a CCD or CMOS image sensoron a test run on a sample of body fluid. The depth of colour of thecontrol and test zones vary over the width and length of the zonesresulting in an uneven appearance. However, in general the depth ofcolour towards the Centre of the zones is deeper than at the outeredges. When the test strip is illuminated by an LED of complimentarywavelengths to the label used, the irregularities of the test andreference zones result in higher optical absorbency at the centre of thezones. Additionally, if the illumination over the length and width ofthe strip is not uniform, the CCD or CMOS image sensor will detectvariations in the reflected lights intensity which are entirelyindependent from the test results.

In order to reduce illumination irregularities and hence suppressspurious test results, multiple error LEDs may be used to illuminate thetest strip. Preferably each LED has an individually adjustable current.CPU 80 may be used to control the current supply to each LED to reducesuch illumination irregularities and hence improve test results.

A further cause of the irregular appearance of the zones as detected bythe CCD or CMOS image sensor is the variation in path lengths traveledby photons reflected from different parts of the surface or theimmunoassay strip. This effect cannot be eliminated by a fixed patterncorrection algorithm because to be most effective such correction shouldtake account of any slight change of location of the test strip inrelation to the mirror and/or CCD or CMOS sensor. Differences, howeversmall, between screening devices mean that it is not possible to definea single fixed pattern correction algorithm for all devices.

In order to minimise the effects of these variations the CPU 80 maydigitally filter the data once the alignment algorithm has been applied.Data corresponding to the entire test strip including the control zone,test zones and background zones is filtered. Each membrane isrepresented by an array of P×Q pixels where P pixels span the length ofthe membrane (rows) and Q pixels span the width of the membrane(columns). Across the width of the membrane the intensity of pixels ineach column would, under ideal conditions, be identical. In practice,due to one or more of the irregularities described, the intensity of thepixels in each column vary to a greater or lesser degree. Thus theintensity of the pixels in each column are summed and the mean valuestored in a 1-d column intensity data array.

Next, the centre of each of the test, control and background zones isestimated. The amount of marker deposited during the test tends to begreater at the centre of the test and control zones than at the edges ofthe zones. Hence, when the strip is illuminated by an LED of acomplimentary wavelength to the marker, the intensity of the pixelsreaches a local minimum close to or at the centre of each of the testand control zones. The geometry of the test strip being known, it is asimple matter to determine the number of pixels spanned by any one zone.In practice, the test and control zones preferably span 40 pixels.However, zones of widths corresponding to any number of pixelsreasonable to achieve the desired resolution may be used.

The total intensity for each test and control zone is estimated bysumming the data in the 1-d column intensity data array over that zonehaving used the local minimum intensity to locate the centre of thatzone and knowledge of the width of the zone to determine how many dataentries centred around the local minimum entry correspond to thatparticular zone.

Although the method described so far takes into account anyirregularities in the deposit of the marker over the width and length ofthe strip, it does not take into account any illumination or uniformity.This may be achieved using information from the irregularities detectedin the background zones where no marker should be deposited.

The data of the 1-d column intensity data array may be corrupted bynoise and noise reduction is therefore performed. The filter achievesnoise reduction by minimising excessive differences between entrieswhilst retaining the underlying signal (intensity of contrast betweentest zones and background zones). Any MA filter producing a symmetricalresponse (ie one where no spatial displacement or phase-shift is presentin the output) may be used. In the presently preferred embodiment, amoving average filter of window length 3 columns is applied to thearray. Longer window length filters may produce better smoothing of thedata and hence improved noise reduction. The length of the filter windowis limited by the spatial distribution of the coloured particlesdeposited. The window size of the filter must be chosen to be muchsmaller than the spatial distribution of the coloured particlesdeposited. Although longer window length filters produce bettersmoothing, they require a large amount of memory for processing andimplementation is algorithmically less efficient than shorter windowlength filters. However, the smoothing effect achieved by a longerwindow length filter may be approximated by applying a smaller windowlength filter multiple times to the data. The 1-d data array istherefore copied and filtered three times using a moving average filterof window size 3 columns. The output of the filtering operation isretained in memory for use later as the non-interpolated image data.

A second moving average (MA) filter is used to interpolate the data toestimate a white, background level (ie to approximate the data thatwould have been obtained had the test bands not been present). Thesecond filter must have a window length sufficient to span the width ofthe control and test zones. It is applied to the noise reduced dataarray which is outputted from the first MA filter. Preferably, when thewidth of the test and control zones is 40 columns, the width of thesecond MA filter is 41 columns. Preferably, the second MA filter isrepeatedly applied to the array. In one embodiment of the presentinvention, the second MA filter is applied 21 times to the array. Inparticular, applying the second filter a number of times to the dataimproves the interpolation accuracy of the data corresponding to thetest zones. Applying the filter 21 times has been found to beparticularly effective for test zones which span approximately 13elements of the data array. The choice of window length is a compromisebetween a requirement for excessive processing and achieving areasonable estimate of the white background level. The filter shouldpreferably be applied a number of times equal to or larger thanapproximately 1.5 times the width of the test zones in the data arrayentries. On each pass of the second MA filter each value of the dataarray is only updated by the filter output if the filter output isgreater than the current value of that value of the array. If the outputof the filter is smaller than the current value of the array, thecurrent value is retained. This process allows the effect of theabsorbency across the test on control zones to be minimised and acleaner “white” background signal to be estimated. Typically, when thewhite background level is estimated from the 1-d data array (rather thanon the original 2-d data array) the performance of the above describedprocess is superior to alternative methods using interpolation of thebackground by applying a polynomial curve fitting approach. The outputof the second filter is supplied to a third moving average filter.

The third MA filter is applied to the output of the second MA filter toremove any spurious peak values or spikes in the data. The third MAfilter of width 11 columns is preferably applied twice to the array.Preferably, the window length of the third MA filter is chosen to beapproximately equal to the width of the test zones in pixels. When thewidth of the test zones is approximately 13 pixels as in one presentlypreferred embodiment, a choice of 11 for the window length of the thirdMA filter is presently preferred. The processed, white background arrayis then used with the total intensity data generated for each test andcontrol zone to estimate the ratio of intensity in each test zone forthe background zones and the intensity of the control zone to thebackground zone. The resulting ratio for the control zone is thencompared against a pre-set threshold to confirm that an appropriateamount of the marker has been deposited in the control zone to indicatethat the sample has run successfully and that the amount of markerdeposited in the control zone corresponds within limits to the amountexpected. If the results of the comparison are negative, a faultcondition is reported to the user, the results are ignored and a repeattest is required.

It will be readily apparent to a person skilled in the art that thefiltering operation could be performed differently to achieve the sameeffect. For example, the white background signal may be estimated fromthe 2-d data array by using linear estimation of several pixel pairslocated at offsets approximately half the inter-test zone spacing fromthe central pixel whose background value is being interpolated.Typically, these pairs lie in the white background zones between testzones and their mean value gives a good estimate for the backgroundintensity in test zone locations. Interpolation of the 2-d data arraymay be carried out and column totals taken subsequently to form the 1-ddata array. An advantage of this technique is that the location of thewindow of the cartridge (and therefore of the relevant portion of thetest) may be performed more reliably. The test zones are virtuallyeliminated from the 2-d array without introducing other distortionsallowing the periphery of the window of the cartridge to be located moreeasily. This method may be particularly effective at accuratelyinterpolating the background when the test zones are very faint. Fainttest zone colour concentration frequently arises for drug tests wherethe concentration of drug present in the sample is close to thethreshold value which determines whether the test is positive ornegative.

For use in adverse weather conditions, various adaptations (not shown inFIG. 1) to the test cartridge may be provided. A retractable,transparent cover may be provided on the test cartridge to protect theimmunoassay test strip 23 which is otherwise exposed through the window22, for example from exposure to rain. The window is retractedautomatically upon insertion of the test cartridge into the screeningdevice and is redeployed when the test cartridge is removed from thescreening device. As shown in FIG. 9, the run fluid may be contained ina trough 68 within the cylindrical swab holder 16 of the test cartridge10. The run fluid is held in place by a thin penetrable membrane 66 thatcovers the trough 68 until the test cartridge is used. The membrane 66is pierced by spike 64 when the membrane 66 is deformed downwardly bythe introduction of a test swab 70 into the swab holder 16. The runfluid is drawn by capillary action across to the conjugate release pad27 via the saliva collection pad 72 of the test swab 70. If the operatorexerts too much force on inserting the test swab 70 into the swab holder16, the membrane 66 may rupture in an explosive manner causing the runfluid to be splashed onto the conjugate release pad 27 without firstpassing over the saliva collection pad 72. If the operator does not useenough force on inserting the test swab 70 into the swab holder 16, themembrane may not be pierced by the spike 64 and the test will not run.These problems are minimised and operator error reduced or eliminated byproviding an internal thread on the bore of the swab holder 16 and thehandle 74 of the test swab 70 may be provided with an external thread.The saliva collection pad 72 is placed into the swab holder 16 and thehandle 74 of the test swab 70 is screwed into the swabholder 16 until itreaches an end atop. This allows controlled piercing of the membrane 66on trough 64 and hence the controlled release of the run fluid to thesaliva collection pad 72.

A second, elastic membrane with an aperture may be positioned above therun fluid membrane in the cylindrical swab holder 16. The aperture ofthe elastic membrane expands to allow a test swab to be inserted throughthe aperture and would form a waterproof seal around the test swab 70prior to the test swab piercing the run fluid membrane. Upon removal ofthe test swab 70, the aperture of the elastic membrane contractspreventing fluid, other than that on the test swab, from entering thetest cartridge.

FIG. 10 shows a cut away side view of a second embodiment of a test swabwhich incorporates both the spike 64 and the run fluid within the testswab, and thus removes the need for these to be provided in the testcartridge.

The handle 74 of test swab 70 is made from a transparent outer tube 78open at the lower end thereof and closed at the top end thereof. At thelower end of the outer tube 78 a flange 76 is provided which protrudesoutwardly from the outer tube 78. The flange 76 may extend around theentire periphery of outer tube 78 or may extend only around part orparts of the periphery of outer tube 78. An adequate spike 64 extendsfrom the closed top end of the outer tube 78 downwardly. Alternatively,instead of a spike, a pin or any other sharp protrusion may be used.

A saliva collection pad 72 is attached to the lower end of tube 79. Thetube 79 is open at both ends. The diameter of the bore of the tube 79 islarge enough to allow the spike 64 attached to the outer tube 78 toenter the bore. Adjacent to the saliva collection pad 72 inside the boreof tube 79 are positioned in order a filler pad 101, dye release pad102, a dye receptor pad 100 and a run fluid capsule 68′. In theembodiment shown in FIG. 10, the run fluid chamber 68′ is a capsule. Therun fluid capsule 68′ is positioned closest to the upper end of theinner tube 78. The tube 79 has a diameter slightly less than theinternal diameter of the outer tube 78 such that the tube 79 may bepositioned within the outer tube 78 and moved vertically relative to theouter tube 7 a. To assemble the swab, as spring 77 is placed in theouter tube 78 through the open lower end and the tube 79, whicheffectively forms an inner tube, is inserted into the outer tube 78 tohold captive the spring 77. In the assembled position, the saliva pad 72and lower part of the tube 79 encasing the filter pad 101, dye releasepad 102, dye receptor pad 100 and run fluid capsule 68′ protrude belowthe lower end of the outer tube 78. The spike 64 is held remote from thecapsule 68′. In this sampling position, the swab may be used to collecta sample of bodily fluids. The length of the spike is determined by themaximum displacement of the tube 79 relative to the outer tube 78 suchthat the spike 64 may be used to puncture the run fluid capsule 68′ whenthe tube 79 is forced, against the pressure of the spring 77, into theouter tube 78. The tube 79 is transparent and the outer tube 78 may alsobe transparent.

With the elongate spike held in the sampling position (i.e. disbursedfrom the capsule 68′), a saliva collection pad 72 of the test swab 70 isinserted into the mouth of the person to be tested and saliva collecteduntil the saliva migrates by wicking effect up the saliva collection pad72 through the filter pad 101, through dye release pad 102 where itbecomes coloured by the dye and into the dye receptor pad 100. Once thedyed saliva becomes visible on the dye receptor pad 100, the user isalerted that an adequate sample of saliva has been collected. The userthen takes the test swab 70 and inserts it into the swab holder 16 ofthe test cartridge 10. As shown in FIG. 11, once the saliva collectionpad 72 of the test swab 70 contacts the conjugate release pad 27 of thetest cartridge, the tube 79 is prevented from being further inserted.Continued pressure on the outer tube 78 of the test swab 70 causes theouter tube 78 to move downwardly relative to the stationary tube 79against the pressure of the spring 77 moving the elongate spike from thesampling position to the sample transferring position. As the outer tube78 is depressed relative to the tube 79, the spike 64 moves downwardlyin the bore of the tube 79 and pierces the capsule 68′ causing the runfluid to move under gravitational force and capillary action through thedye release pad 102, dye receptor pad 100, filter pad 101 and onto thesaliva collection pad 72 where it mixes with the saliva. It is thendrawn onto the conjugate release pad 27 which is in intimate contactwith the saliva collection pad 72. The swab holder 16 is provided at itsupper end with resilient lips 104 which extend inwardly from thecylindrical swab holder 16. The lips 104 define a hole with a diameterwhich is slightly larger than that of the outer tube 78 but smaller thanthe diameter of the flange 76 on outer tube 78. The flange 76 isprofiled such that there is a smooth change in diameter of the flange atthe open end of the outer tube 78 and a more abrupt change at the upperextent of the flange 76 remote from the open end of the outer tube 78.Upon insertion of the outer tube 78 into the swab holder 16, the gradualchange of diameter of the flange 76 forces the resilient lips of theswab holder apart allowing the outer tube 78 to pass into the swabholder 16. Once the outer tube 78 has been inserted to a point justbeyond the extent of the flange 76, the lips of the swab holder 16spring back to their original unstressed position and the outer tube 78is effectively held in position relative to the swab holder 16 of testcartridge 10 preventing the test swab 70 from being accidentally removedfrom cartridge 10 and hence ensuring intimate contact of the salivacollection pad 72 and the conjugate release pad 27 for the duration ofthe test. The filter pad 101 may be used to prevent the dye fromcompromising the test results. Alternatively, a dye may be chosen which,although visible to the human eye, is invisible or nearly so, at the LEDwavelength used by the screening device. The filter pad 101 may alsolimit the rate at which the run buffer is released from the piercedcapsule 68′ to the test cartridge 10, thereby improving the mixing ofthe saliva sample and the run fluid.

FIG. 12 shows a cut away side view of a third embodiment of a test swabwhich is suitable for use with a test cartridge. This embodiment of testswab 70 requires that a spike 64 is provided in the swab holder 16 ofthe test cartridge. As shown in FIG. 14 the spike 64 is attached to aspike holder 65 which in turn is attached to the swab holder 16. Thespike 64 preferably has a cruciform cross-section as shown in FIG. 15.The test swab 70 comprises a saliva collection pad 72, a main tube 108,a run fluid chamber, or capsule, 68′ and an indicator section. Theindicator section comprises a capillary tube 110, a dye release pad 102and a dye receptor pad 100. The saliva collection pad 72 is incommunication with the open base of a main tube 108. The upper end ofthe main tube is also open. A penetrable gelatine capsule 68′ filledwith run fluid is located within the main tube 108 spaced from thesaliva collection pad 72. Disposed to the side of the main tube 108 is acapillary tube 110. A small port 116 is provided in the wall of the maintube 110 a short distance from the saliva collection pad 72. The openlower end of the capillary tube 110 is attached to the main tube 108 atthe port 116 and communicates with the main tube 108 via the port 116.

Provided around the periphery of the lower portion of the main tube 108and capillary tube 110 is a guide 112 and insertion endstop 106. The endstop is spaced from the saliva collection pad 72 substantially the samedistance as the distance from the centre of the capsule 68′ to thesaliva collection pad 72. The guide 112 and end stop 106 may extendaround the whole periphery of the main and capillary tubes 108 and 110or only partially around the periphery.

At the end of the capillary tube 110 remote from the port 116, a dyerelease pad 102 and dye receptor pad 100 are provided. The dye receptorpad 100 is positioned at the open end of the capillary tube 110 and isvisible from the top and/or sides of the capillary tube 110. The dyerelease pad 102 is spaced from the dye receptor pad 100. In operation,as saliva is collected on the saliva collection pad 72, some of it isdrawn up the capillary tube 110 by capillary action where it contactsthe dye release pad 102. The saliva becomes dyed as it passes over thedye release pad 102 and as it travels further up the capillary tube 110it contacts the dye receptor pad 100 which becomes visibly stained bythe dye indicating that an adequate sample of saliva has been collected.The test swab 70 may then be removed from the mouth of the person beingtested and inserted into the test cartridge 10. The guide 112 ensuresthat the test swab 70 is inserted optimally into the swab holder 16 andfurther ensures that the run fluid capsule 68′ will be pierced by thespike 64 of the swab holder 16. The end stop 106 of the test swab 70prevents the user from inserting the test swab 70 too far into the testcartridge and thus prevents the test cartridge from becoming damagedwhich may interfere with the proper running of the test. The user isalerted by the test stop hitting the periphery of the swab holder 16that the test swab 70 is fully inserted and has been advanced far enoughinto the swab holder 16 for the spike 64 to have punctured the capsule68′ thereby releasing the run fluid which mixes with the saliva sampleand is transported by gravitational and capillary action onto theconjugate release pad 27 of the test strip 23. The dye receptor pad 100may be a cotton swab.

The guide 112 may be formed of simple projections with the diameter ofthe swab measured across the projections being slightly smaller than thediameter of the swab holder 16 such that when the swab is inserted intothe swab holder 16 the guide 112 causes the swab to be centred in theswab holder 16. Alternatively the guide 112 may consist of an externalthread arranged around the periphery of the main and capillary tubes 108and 110 and co-operating with an internal thread provided on the bore ofthe swab holder 16. If the guide is provided by an external threadedportion then the end stop 106 may be omitted and the swab inserted untilthe end of the thread is reached determining the final position andpressure of the spike 64 on the capsule 68′. Other embodiments of thetest swab may be provided.

Although described with reference to lateral flow immunoassay testing,the above described test swabs could be is used to take a sample ofsaliva for agglutination testing. The difference being that instead ofthe saliva/run fluid mixture being drawn over a conjugate release padand thereafter onto and along a nitrocellulose test strip, anagglutination test cartridge is provided.

The screening device may also be used to detect the results ofagglutination tests. Agglutination tests are generally categorised intoone of two categories depending on the size of the analyte whosepresence is to be detected. The screening device may be used todetermine the results of both agglutination categories.

In the first category, large analytes with multiple epitopes (bindingsites) such as proteins can be detected. Coloured (or white) latex beads(microspheres or nanospheres) are coated with antibodies to the protein,suspended in an appropriate buffer solution, mixed with the sample undertest and the mixture incubated. The presence of the antigen (ie theanalyte whose concentration or presence in the sample is being testedand to which the antibodies are directed) in the sample causes multiplelatex beads to bind together by bridging between two antibodies coatedto different beads. Because the proteins (or other large molecule undertest) are capable of binding with more than one antibody at a time dueto their multiple epitopes and each latex particle has multipleantibodies coated to it, then complexes of beads are formed causingagglutination. Huge molecules, which are discernible to the naked eye,are formed by the large scale clumping. These molecules may be detectedby the screening device and the relative concentration of the substanceunder test may be calculated. Use of the screening device allows thesensitivity of the test to be increased because individual pairs ofbound latex beads (dimers) can be detected by using imaging apparatuswith sufficient optical magnification.

There are further advantages in using the screening device for thesecond category of agglutination reactions. In this second category,sometimes referred to as agglutination inhibition reactions, smalleranalytes such as drugs can be detected. Coloured (or white) latex beads(or polystyrene beads or liposomes) which are irreversibly attached todrug molecules are manufactured. Free antibodies are mixed with thesample under test and then added to the coloured latex beads. If thereare no drug molecules present in the sample, the antibodies bind withthe coloured latex beads forming bridges between beads and agglutinationwhich results in localised high concentrations of coloured latex beadswhich can then be detected. However, free drug molecules in the samplewill compete for binding sites on the free antibodies with the drugbound latex beads. Hence, if a sample contains a drug being tested for,the drug molecules bind to the free antibodies which are not then freeto bind with the latex beads, hence presence of the drug inhibits theagglutination which would otherwise occur. The absence, or reduction, ofagglutination can be detected and the concentration of the drug in thesample may be calculated.

Other variants of these agglutination reactions such as using the deviceto monitor the rate of agglutination or the use of different types ofparticle or different reaction mechanisms will be obvious to thosefamiliar with this field.

An embodiment of the screening device may also be used to screenagglutination reactions. In order to determine the results of anagglutination test, regions of (bio) chemical coagulation oragglutination (hereafter referred to as condensates) must be uniquelyidentified, counted, measured in area, colour and/or intensity andgenerally distinguished from one another. In the digitised image, thecondensates of interest are generally larger than a single pixel andadjacent pixels belonging to the same condensate must be recognised assuch. Distinct condensates must be differentiated. There are varioussources of noise in the digitised image. Fixed pattern and random(statistical) distortions are introduced by the optical components.Spatial location and variations due to manufacturing tolerances of theComponents of the screening device also introduce random errors.Compensation for these errors is provided by the screening device.Correction for non-uniform illumination and differing imaging parameters(such as exposure and amplification) and variations in theconcentrations of the test sample and reaction chemistry may also becorrected. Objects within the image which are too small, too large or ofa particular shape may be disregarded. In the preferred embodiment, theinstrument is hand held and powered by batteries. The image processingis capable of producing results accurately and rapidly using moderatecomputer processing and memory resources.

FIG. 21 shows the plan view of a single reaction agglutination testcartridge. The test cartridge 10′ is made of three sandwiched plasticlayers. The middle layer defines the sides of the channel 230, the sidesof the reaction chamber or chambers 232 and the sides of the overflowreservoir 234. The top layer defines holes forming venting holes 236 tothe overflow reservoir 234 when the layers are assembled. The top layeralso defines an entry port 16′ into which the sample may be inserted.The entry port 16′ communicates with the channel 230 provided in themiddle layer. The bottom layer and top layer form the bottom and toprespectively of the channel 230, reaction chamber 232 and overflowreservoir 234.

As described above, a sample of bodily fluid such as saliva ispre-processed by mixing with free antibodies to the drug under test andcoloured latex beads which are irreversibly attached to the drugmolecules under test, and the mixture applied to the test cartridge 10′using entry port 16′.

The sample is drawn from the entry port 16′ along the channel 230. Thechannel is designed to have a length which allows time for anypre-processing reactions to occur. Once it has passed the length of thechannel 230, the sample enters the reaction chamber 232 whereagglutinates develop. An overflow reservoir 234 is provided in the testcartridge 10′ and communicates with the reaction chamber 232. Once thereaction chamber is filled by the sample, excess sample moves to theoverflow reservoir 234 which has venting holes 236 which are exposed tothe atmosphere. The excess sample may therefore escape from the testcartridge 10′ preventing pressure build-up inside the cartridge.

A window is provided in the top of the reaction chamber 232 and thewindow is illuminated by the screening device to detect the results ofthe agglutination reaction. Alternatively, the entire test cartridge 10′may be made from a plastics which is transparent to the wavelength oflight used by the screening device.

FIG. 22 shows an agglutination test cartridge used to evaluate thepresence or absence of multiple analytes. In addition to a plurality ofreaction chambers 232, the test cartridge 10′ provides a plurality ofreactant chambers 238. Each reactant chamber 238 holds a supply ofcoloured latex beads irreversibly bound to molecules of the drug forwhich the test is being conducted. The reactants are held in animmobilised state for example by freeze drying. The saliva sample to betested is mixed with free antibodies to the drug under test and suppliedto the test cartridge 10′ via the entry port 16′. The saliva/freeantibody mix passes along the channels 230 into the reactant chambers238 where it mixes with the coloured latex beads. The mixture thenpasses to the corresponding reaction chamber 232 where any agglutinationreaction occurs. By using coloured latex beads bound to different drugmolecules in each reactant chamber 238, the presence of a number ofdifferent drugs can be detected using a single test cartridge 10′. Eachreaction chamber 232 communicates with the overflow reservoir 234 whichhas venting holes 236 exposed to the atmosphere. The reactant chambers238 may be placed in series or in parallel as required by the test. Inthe embodiment of test cartridge 10′ shown in FIG. 22, saliva/freeantibody mixture is supplied directly to two of the three reactantchambers 238 with the third reactant chamber 238 being supplied with themixture from one of other reactant chambers.

Alternatively, the reactant chamber 238 could hold a sample of freeantibodies to the drug under test and the coloured latex beadsirreversibly bound to the drug under test could be mixed with the salivasample before the mixture is supplied to the entry port 16′. Threereaction chambers 232 are provided and the channel 230 bifurcates toallow entry of the sample to two of the three chambers 232. The thirdchamber is supplied with sample directly from one of the other chambers.

Windows are provided in the top of each of the reaction chambers andwhen processing the data using an embodiment of the screening device,preset data is provided to give the location of the different reactionchambers.

The image processing for agglutination reactions will now be describedwith reference to FIGS. 16-19.

FIG. 16 shows a flow chart of the screening operation. The maindifference between testing for an agglutination reaction and for animmunoassay test is that the CPU processes the digitised image in adifferent manner. The hardware of the screening device may be identicalfor screening immunoassay tests and agglutination reactions.Alternatively, the agglutination reaction may use a different size oftest cartridge and the opening in the screening device may be adapted toaccommodate the agglutination reaction test cartridge. An adaptor may beprovided to allow two or more sizes or types of test cartridge to beused.

The image is acquired, digitised and the data stored to a 2-D array(120) by the imaging section of the screening device. The data arrayrequires around 102 KB of memory (356×292 pixels×8 bits per pixel). Thedata processing can be conducted using a small amount of additionalmemory of say 8 KB thus eliminating the need for providing memory for asecond array. The screening device is therefore provided with commonlyavailable 128 KB static RAM, Fixed pattern image distortions are removedby applying various two-dimensional transformations to the data (122).These techniques can be used to remove tilt, trapezoidal, rotation,translation, pin-cushion (where the appearance of the image is distortedso that the centre of the image appears to have been pulled upwardly outof the plane of the image) or barrel distortion (where the appearance ofthe image is distorted so that the centre of the image appears to havebeen pushed downwardly through the plane of the image) of the image.Suitable 2-d transformations are simple mathematical equations formapping the points of the distorted image to the corresponding points onthe original object. If a continuous transformation is determined, itmust be discretised for implementation in the processor. Alternatively,the transformation which maps the original image onto the distortedimage may be estimated, in which case the inverse transformation must becalculated for application in the processor.

For agglutination test, the number of small condensates can be large andthe accuracy of the result is limited by image resolution anddistortion. It is therefore desirable to transform the image prior toany further processing to permit image scaling and the removal ofdistortion to be consistently achieved. By measuring for each image thelocation of the corners of the test window and the mid-points of thetest window edges, an algorithm may be developed which calculates themathematical transformation necessary to achieve a target window size,position, rotation and distortion.

Once any imaging distortions have been corrected, noise reduction (124)is performed by applying a 2-D low pass filter to the data. Once thedata has been filtered, histograms of pixel intensities for the entirearray are created (126). If necessary, histograms of pixel intensitiesof sub-sections of the array may be created. Using the pixel intensityhistograms and knowledge of the underlying chemistry of theagglutination reaction, threshold intensities for sub-sections of theimage are produced (128). For example if 20% of the image area isnormally occupied by condensates, then the histogram can be used todetermine the pixel intensity thresholds to divide the image sectionsinto two portions, one approximately four times as large as the other.This information is test specific and is stored on preset data in thememory of the screening device. Once the thresholds have beendetermined, they are applied to the array to transform it into amonochrome 2-d array (130). Depending upon the chemistry involved,portions above (or below) the threshold value determined for each imagesection are interpreted as agglutination condensates or backgroundregions. Condensate areas are then represented by negative integervalues and the background regions by a zero value. Different imagesub-sections may be represented by different negative integer values.

The monochrome array is first processed to identify the backgroundregions (zero valued entries) and a plurality of positively valuedentries which closely approximate the location of the condensates (132).Flow charts for processing the monochrome array to identify backgroundregions and condensates are shown in FIGS. 17 and 18. FIG. 18 is a flowchart showing the processing of the data during the scan. The imagearray address registers X and Y are initialised to zero (160). A currentblock register is initialised by setting the value to one (162). Themonochrome array is sequentially processed. The order in which the arrayis processed is shown in FIG. 17.

FIG. 17 shows the sequence of the raster scan. Processing commences withthe data which corresponds with the bottom lefthand corner of the image,works along one column of the agglutination test, moves to the adjacentrow and starts processing the entries corresponding to the next column.

The elements are referenced by (X,Y) where 0≦X≦Xmax and 0≦Y≦Ymax with Xincrementing column-wise from left to right and Y incrementing row-wisefrom bottom to top. Elements in the array which store negative integerscorrespond to condensate areas.

As each element is accessed a check is made to determine whether thevalue stored in that element is negative (164). If the element isnegative, the value of element is set to the value of the current block(166). The value of the current block is increased by one (168). Thesurrounding elements of the array which have already been scanned areidentified. For example FIG. 17 shows as the current position elementthe central element. The adjacent previously scanned elements are thosenumbered 12, 7, 8 and 9. The values of these previously scanned adjacentelements are compared with each other and with the value of the currentelement. The smallest non-zero positive value of the current element andpreviously scanned adjacent elements is stored (170). Assuming that thisvalue is stored as Z, the current block value is compared to the valueof Z+1(172). If the value of Z+1 is smaller than the value of thecurrent block all non-zero positive elements among the previouslyscanned adjacent elements and the current element are tagged (174), thatis the value stored in the element is set to the value Z, the currentblock is decreased by one (176) and the processor moves on to considerthe next element in the array (180, 182 and 184). If the value of Z+1 islarger than or equal to the value of the current block then the currentelement pointer is incremented by one (178) and the processor moves onto consider the next element in the array. Processing continues untileach element of the array has been processed in this manner (180, 182,184).

Some of the condensates within the array will have been identified morethan once by the above processing and areas of a single condensate mayhave different values or “tags”. Where more than one tag relates to asingle condensate, further processing to resolve the discrepancy isrequired. Tags which are equivalent, ie relate to the same condensate,must be identified and the information used to amend the array such thatthe same tag is used for each distinct condensate but differentcondensates are identified by different tags. A 1-d “tag tree” array isconstructed (134). The length of the tag tree array is set by the valueof the final current block from processing the monochrome array. Forexample, if the current block is say 5 after finishing the firstprocessing, the tag tree array is a (1×5) array. The tag tree array isinitialised such that each element references itself i.e.array(element)=element. Each tag (condensate label) is therefore mappedonto itself. By modifying the elements of the tag tree array, it ispossible to identify equivalent tags. To do so, the processed monochromearray is processed a second time.

FIG. 19 shows a flow chart of the second processing operation. Theprocessed monochrome array is processed element-wise in the same manneras described with reference to the first processing. For each element,the values of the current element and those previously processed arrayelements adjacent to the current element are compared (192). If anypositive, non-zero entries are found, the lowest value is selected andstored in the tag tree array element corresponding to the higher valuetag or tags (196). For example if the current element has a value 3, andthe adjacent elements which have already been processed have the values2, 3 and 4, then the value 2 is stored to the third and fourth tag treeelements. The equivalence between tags is thus recorded.

The elements of the 1-d tag tree are scanned from the first entry to thelast and updated. FIG. 20 indicates the processing carried out. A tagtree address register X is initialised by setting all the entries tozero. X is valid over the range 0 to Xmax where Xmax is equal to oneplus the number of elements in the tag tree array (210). The current tagtree entry is stored to a storage register Y (212). The element of thetag tree array corresponding to the value stored in storage register Yis accessed and its value stored in register Z (214). The current tagtree entry (X) is set to the value of register Z (216) and the Xregister incremented to process the next tag tree element (218) untilall elements have been processed (220). For example for a 1-d tag treecontaining a thousand entries numbered 1 to 1000 the initialised arrayis TREE[LEAF]=LEAF. After initial processing, it is possible for someentries (leaves) to be equivalent to others. For example, TREE[752]=329,TREE[839]=329, TREE[329]=78 and TREE[78]=78. Entry 78 is equivalent toitself and is therefore a primary leaf. The remaining entries of thisexample can be related to the primary leaf by a branch[752,839]-[329]-[78] being the branch in this example. Scanning the tagtree decomposes the entries to leave all the entriesTREE[752]=TREE[839]=TREE[329]=TREE[78]=78. The entries of the tag treeare then limited to primary leaf values thereby eliminating branchvalues and setting all the entries of a branch to the same value.

When the scan is completed, only legitimately distinct “leaves” of thetree remain; the branches linking the leaves have been eliminated. Theleaves are not necessarily contiguously arranged nor are theynecessarily in ascending numerical order.

Referring now to FIG. 16, a tag usage array of identical length to thetag tree array is initialised by setting all the elements to zero (140).Each element of the updated tag tree is checked to see whether it isnon-zero. For each non-zero value of the tag tree, the correspondingarray element of the tag usage tree is set to one or any non-zero value(142). The current block register is then used to consecutively numberthe tag usage tree values. The current block register is set to one. Inan element-wise fashion, each element of the tag usage tree is comparedto zero and each time a non-zero entry is found, its value is set to thevalue of the current block register which is then incremented (144).

The tag tree is then updated once more using the tag usage array. Thevalue of the current tag tree array element is used to reference thecorresponding tag usage tree element. The value of the current tag treearray element is replaced by the value of the referenced tag usage treeelement (146).

Once the tag tree has been updated, the elements are compared and thehighest positive value indicates the number of distinct condensatesdetected in the original image (148). The processed monochrome array canbe updated using the tag tree array (150). The array is processedelement-wise as before and where the value stored for an element ispositive and non-zero a check is made of the tag tree array to determinewhether or not the value should be amended. Assuming the current elementof the processed monochrome array is N and the value stored therein is3, the third element of the tag tree array is accessed. The value storedin the third element of the tag tree array is then stored at the Nthelement of the processed monochrome array. The twice processedmonochrome array now represents the background regions denoted byzero-valued entries and contiguously numbered distinct condensatesdenoted by contiguous positive numbers. The condensates may beclassified according to their size and relative frequency by countingthe number of entries with the same positive non-zero values in thetwice processed monochrome array (152).

The results obtained are used to determine whether the sample containedthe analyte(s) being tested for (154). In the simplest case, theagglutination test measures just one analyte. For standard tests, highnumbers of large agglutinates indicate a positive result whereas forinhibited agglutination reactions, this indicates a negative result.Depending on the properties of the noise reduction filter (124) andthreshold determination (128), large numbers of small agglutinates mayor may not be obtained. Therefore, the agglutinates may have to becategorised according to their size. This is achieved by performing afinal image scan in which the number of times a particular tag occurs isrecorded in a new data array. Agglutinates of size smaller than a givenvalue are indicated by the new array having a value less than thethreshold. These agglutinates may be disregarded in the results of thetest.

In a manner similar to that of processing the results of agglutinationtests, the screening device may be used to determine the outcome ofprecipitation reactions, reactions based on electrophoresis,immunoelectrophoresis, immunofixation electrophoresis, enzymeimmunoassay and immunofluorescence. Any of these techniques may beadapted to allow the screening device to differentiate between thepresence and absence of analyte in a patient sample by appropriate imageprocessing. For certain reactions, the test may be designed to produce acolour change which can then be detected by the screening device.Kinematic analysis may be used both to determine the rate of change incolour and to determine the final test result. The screening device iscapable of performing many kinds of kinematic analyses. Combinationtests may be provided with the test bands for multiple analytesco-located on the test strip by ensuring the optical absorbency of eachtest is independent. The screening device may then differentiate betweenthe independent test bands by scanning first with one optical wavelengthand then with the next wavelength.

Channel-based reaction sequences may be designed such that intermediatereaction products deposited on the nitro-cellulose strip may be detectedoptically as the reaction progresses. Intermediate reaction products mayallow for a reliable early warning of the test results before the testhas been completed.

The latex beads may be bound to either analyte (drug), antibody or both.Bonds can form between two analytes via an intermediary, or carrier,molecule known as a protein bridge (for example polylysine). Reactionsmay be organised into one of two classes: competitive ornon-competitive. These classes are akin to the distinction betweenagglutination and inhibition of agglutination reactions.

Kinematic analysis, where the rate of change in colour is determined,may also be undertaken by the screening device. The screening device maybe provided with a plurality of illumination sources of differingwavelengths. Combination tests can be designed such that the test bandsfor multiple analytes are co-located but the optical absorbency isindependent such that the screening device can differentiate between theresults for the multiple analytes by illuminating the test strip withdifferent wavelengths of light successively.

Instead of providing printed test zones spanning the entire width of thenitro-cellulose strip, it is possible to print an array of dots witheach separate dot comprising a test zone for a different analyte. Wherethere are only a small number of analytes to be tested, the separatedots and the control band or dots may be printed closer to the conjugaterelease pad to reduce the run time of the test.

It is also possible that an assay test is designed whereby intermediatereaction products are deposited during the reaction process. Thesereaction products may be detectable prior to the completion of the testand in certain circumstances, it is desirable to provide an early outputwhere the results of the test can be reliably reported using theintermediate reaction products.

With respect to the above description, it is to be realized thatequivalent apparatus and methods are deemed readily apparent to oneskilled in the art, and all equivalent apparatus and methods to thoseillustrated in the drawings and described in the specification areintended to be encompassed by the present invention. Therefore, theforegoing is considered as illustrative only of the principles of theinvention. Further, since numerous modifications and changes willreadily occur to those to skilled in the art, it is not desired to limitthe invention to the exact construction and operation shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be resorted to, falling within the scope of the invention.

For example, in alternative embodiments of the invention, the sample tobe tested could include urine, serum, plasma, ocular fluid or filteredwhole blood. Suitable filtering systems for whole blood could beincorporated into the cartridge. The screening device could also used inother areas of immunodiagnostics. For example, the screening devicecould be used to analyse the concentration of tumour markers in theblood samples of patients undergoing treatment for cancer. The screeningdevice could also be adapted for use to measure the levels of hormone,or therapeutic drug present in a sample or to test for bacteria, virusesor other microorganisms present in a variety of sample types.Alternatively the screening device could be adapted to screen samplesfor allergies.

It should be noted that the features described by reference toparticular figures and at different points of the description may beused in combinations other than those particularly described or shown.All such modifications are encompassed within the scope of the inventionas set forth in the following claims.

1. A method of conducting and screening an agglutination test toidentify the presence of an analyte in a sample, said test producingareas of agglutination and background areas, said method comprising thesteps of: mixing said sample with one or more agglutination reactantsand flowing the sample and reactant mixture through a channel whereby anagglutination reaction or agglutination pre-processing reaction occursin the channel; receiving the mixture in a reaction chamber where anagglutination reaction occurs or is completed; illuminating saidreaction chamber; detecting the intensity of light which is reflectedfrom said areas of agglutination and background areas of said reactionchamber; representing the intensity of said detected light in adigitised data array; determining a threshold intensity or intensitiesusing the distribution of pixel intensities across said data array, andusing the threshold intensity or intensities to threshold said dataarray to distinguish between background areas and areas ofagglutination; identifying areas of agglutination and estimating thenumber of said areas of agglutination; determining whether said areas ofagglutination exhibit a statistically significant result; and outputtingsaid results.
 2. A method according to claim 1, including the step ofperforming noise reduction of said digitised data array prior tothresholding said digitised data.
 3. A method according to claim 1,wherein: said step of detecting the intensity of light reflected fromsaid areas of agglutination and background areas of said reactionchamber is carried out by an array of photosensitive detectors; saidstep of thresholding said digitised data being carried out in athreshold processor which is coupled to the output of a digitiser; saidstep of identifying areas of agglutination being carried out in a firstdata processor which is coupled to said threshold processor; and saidstep of determining being carried out in a second data processor whichis coupled to the output of said first data processor.
 4. A methodaccording to claim 1, wherein said step of mixing said sample with oneor more agglutination reactants comprises mixing the sample with anantibody to said analyte.
 5. A method according to claim 1, wherein saidstep of mixing said sample with one or more agglutination reactantscomprises mixing the sample with beads coated with said analyte oranalyte component.
 6. A method according to claim 5, wherein saidanalyte is a viral antibody and said analyte component is a viralantigen.
 7. A method according to claim 1, wherein said step of mixingsaid sample with one or more agglutination reactants comprises mixingthe sample with an antibody to said analyte and with beads coated withsaid analyte or analyte component.
 8. A method according to claim 1,wherein the at least one of the agglutination reactants is held in animmobilised state in a flow path, the method comprising hydrating theimmobilised agglutination reactant(s) with said sample as the sampleflows along said flow path.
 9. A method according to claim 1 comprisingseparating the sample into a plurality of channels each containing anagglutination reactant in an immobilised state, flowing the samplethrough the channels to hydrate the immobilised reactants, and receivingthe flows in respective reaction chambers.